1. Field of the Invention
This invention relates to a circuit for generating a signal for a predetermined time interval after a power switch is opened.
2. Description of the Prior Art
In the case of a conventional latching relay, for example, a contact is closed when a conduction signal is supplied and the contact is kept closed even after the conduction signal is cut off; and the contact is opened if a nonconduction signal is subsequently supplied and the contact is kept in the same situation until the next conduction signal is supplied. In such a case, if a power switch of a signal generating device is opened after a conduction signal is applied, the contact of the latching relay is kept closed since a nonconduction signal will not be supplied thereafter.
However, it is sometimes very desirable that the latching relay is maintained in a nonconductive situation whenever an operator turns off the power switch.
Further, in the case of a RC integrating circuit, for another example, when a time duration required to raise a terminal voltage of an integrating capacitor up to a predetermined value from its initial state where said terminal voltage of the integrating capacitor is zero is measured and its charging time is used for a particular purpose, a certain amount of electric charge is held on the capacitor if the power supply of the RC integrating circuit is interrupted before the terminal voltage across two terminals of the capacitor reaches the predetermined value.
When the power switch is closed again after a period of time, a disadvantage is noted in that the time required to charge up the capacitor to the predetermined voltage is shorter than normal value because the capacitor retains some residual charge before it is charged again. Thus, it is necessary to bring down the capacitor terminal voltage to zero (initial condition) whenever the power source is switched off.